The invention relates generally to systems and methods for determining whether a live human finger is being applied to a fingerprint sensor or other sensing device. In particular, the described systems and methods prevent unauthorized users from “spoofing” a fingerprint sensor by creating artificial fingers that replicate the fingerprint pattern of a valid user.
Fingerprint sensors are seeing increased usage in many devices, such as laptop computers, cell phones and other mobile devices, and security systems for the purpose of user authentication and password replacement. This increased usage of fingerprint sensors has raised concerns about the level of security provided by these sensors. One concern involves the creation of artificial fingers that replicate the fingerprint pattern of a valid user and are applied to the fingerprint sensor to gain unauthorized access to a device, building, and the like. These artificial fingers are often created using materials that are electrically and optically similar to live finger tissue. Materials commonly used to create artificial fingers include gelatins, rubbers, and glues.
Several techniques have been developed in an attempt to detect the electrical differences between live human fingers and artificial fingers created for the purpose of “spoofing” a fingerprint sensor. Most of these techniques try to differentiate live fingers from artificial fingers by attempting to detect small differences in internal electrical impedance values that are measured by electrically contacting the finger. For example, existing techniques measure the capacitance of an object and determine whether the object's capacitance is within a range associated with the biological characteristics of live finger tissue. Other similar techniques measure the resistance or electrical impedance of an object instead of the object's capacitance.
These existing techniques are used with limited success due to the wide variations in capacitance, resistance, and impedance of human tissue over large populations and demographics. These wide variations prevent the establishment of accurate boundaries for detecting live fingers without increasing the false rejection rate of the detection system. Additionally, the capacitance, resistance, and impedance of human tissue varies over time for a particular user and changes in response to environmental conditions. For example, the resistance of a user's finger changes in proportion to sweat gland activity in the user's finger. Additionally, dermatological conditions, diet, and exposure to certain chemicals can alter the capacitance, resistance, and impedance of human tissue.
Throughout the description, similar reference numbers may be used to identify similar elements.